The most recent spacecraft telemetry was acquired on Dec. 8 from the
Deep Space Network tracking complex at Madrid, Spain. The Cassini
spacecraft is in an excellent state of health and all subsystems are
operating normally. Information on the present position and speed of
the Cassini spacecraft may be found on the "Present Position" page
at: http://saturn.jpl.nasa.gov/operations/present-position.cfm.
Wednesday, Dec. 2 (DOY 336)
This week the Composite Infrared Spectrometer measured oxygen
compounds -H2O, CO2 - in Saturn's stratosphere as a function of
latitude, and performed mid-infrared mapping of Saturn to determine
upper troposphere and tropopause temperatures with spatial resolution
of about two degrees of latitude and longitude. Imaging Science
(ISS) took wide-angle camera photopolarimetry images, images of
Iapetus, and searched for lightning on Saturn. The Magnetosphere and
Plasma Science instruments continued observations in support of the
solar wind-aurora and magnetospheric boundaries campaigns. The Visual
and Infrared Mapping Spectrometer, along with ISS, performed another
E/G ring phase observation and looked at Saturn global dynamics.
Thursday, Dec. 3 (DOY 337)
A kick-off meeting was held today as part the S55 DOY 343 Radio
Science (RSS) Live Movable Block (LMB) process. After a quick
turnaround by Navigation, Science Planning, and RSS, it was
determined that no further work was needed on the current product
that had been developed along with the background sequence and
delivered in mid November. The command approval meeting and uplink
are set for Monday of next week.
Friday, Dec. 4 (DOY 338)
Orbit Trim Maneuver (OTM) #225 was performed today. This was the
apoapsis maneuver setting up for the Titan 63 encounter on Dec. 11
(Dec. 12 GMT). The Reaction Control Subsystem burn began at 1:00 AM
PST. Telemetry immediately after the maneuver showed a burn duration
of 180.38 seconds, giving a delta-V of 201.6 mm/s. All subsystems
reported nominal performance after the maneuver.
Monday, Dec. 7 (DOY 341):
Commands were uplinked to the spacecraft today for the RSS LMB due to
execute on DOY 343, and to set the value of the Command Loss Timer
(CLT) to 5 days. The RSS passes on DOY 343 have no uplink
capability. If for some reason Cassini were to lose the next
scheduled pass on DOY 345, we would exceed the current value of the
timer and safing would be called. The value was extended to 5 days
"just in case" and will be set back to the nominal value of 90 hours
on Friday, Dec. 11.
Today the Navigation team proposed the cancellation of OTM-226, the
Titan 63 approach maneuver due to execute on Dec. 8. After OTM-225,
the flyby target miss at T63 was about 2 km. This small miss resulted
in OTM-226 magnitude estimates that were below the minimum delta V
threshold, thus requiring a bias in the time of closest approach to
achieve an implementable maneuver. Science Planning determined that
the pointing errors would be well within acceptable margins if the
OTM were cancelled, and no Live Update would be necessary. The
delta-V cost of 0.1 m/s for cancellation was deemed acceptable.
Therefore OTM-226 has been cancelled.
Tuesday, Dec. 8 (DOY 342)
The Science Forum for S60 was held today. Topics included an overview
of science planned for this sequence followed by highlights, unique
activities, and highest priority observations provided by the Target
Working Teams and Orbiter Science Team leads, with comments from the
Investigation Scientists and other instrument team representatives.
In an encore performance from 2005, an image of Tethys was Astronomy
Picture of the Day today. Check it out at:
http://antwrp.gsfc.nasa.gov/apod/ap091208.html
Preview, Dec. 9 (DOY 343)
After waiting years for the sun to illuminate Saturn's north polar
region, Cassini has captured the most detailed images yet of the
intriguing hexagon shaped feature that surrounds the pole. The new
images of the hexagon reveal concentric circles, curlicues, walls and
streamers not seen in previous images. Images and a three-frame
animation are available at
http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20091209/
A pair of moons and a pair of moon shadows can be seen in a Cassini
image taken about a month and a half after Saturn's August 2009
equinox crossing. Pan orbits in the Encke Gap of the A ring, and it
can be seen casting a shadow near the center of the image. The moon
Janus, which is not visible, is casting its shadow on the A ring in
the top right of the image. Pandora can be seen orbiting beyond the
thin F ring in the top left of the image, but its shadow doesn't
accompany it here. For the full text and to view the images link to:
http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=3767
In the December release of the Cassini Science League, the reader is
presented with the question: Methane on Titan and Enceladus: Nature
vs. Nurture? Direct samplings of Titan's atmosphere and Enceladus'
plume have provided key measurements for determining the original
recipes for these moons. A key question has been whether these two
moons formed initially with methane as part of their chemical make-up
or whether methane formed in Titan and Enceladus over time. For the
full text link to:
http://saturn.jpl.nasa.gov/news/cassiniscienceleague/science20091207/
. For additional Science League articles go to:
http://saturn.jpl.nasa.gov/news/cassiniscienceleague/
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